1. Field of the Invention
The present invention relates to a damage evaluation method of a compound semiconductor member, a production method of a compound semiconductor member, a gallium nitride compound semiconductor member, and a gallium nitride compound semiconductor membrane.
2. Related Background Art
Compound semiconductors have various merits in comparison with Si. For example, the compound semiconductors permit control of the bandgap through adjustment of compositions. Furthermore, the compound semiconductors have such optical properties as direct transition and wide bandgap, and are thus suitably applied to optical devices such as LEDs or LDs. Since the compound semiconductors have high carrier mobility, they are also suitably applied to high-speed devices.
In producing such compound semiconductor devices as the optical devices or high-speed devices, a substrate used is a compound semiconductor substrate, or a laminated substrate in which a compound semiconductor membrane is formed on an amorphous substrate such as a glass substrate. For example, a compound semiconductor membrane or electrodes are formed on a surface of the compound semiconductor substrate or laminated substrate. The device characteristics of the compound semiconductor devices are significantly affected by an interface between the compound semiconductor substrate or laminated substrate and the compound semiconductor membrane or by interfaces between the compound semiconductor substrate or laminated substrate and the electrodes. Therefore, it is important to evaluate the interfaces in the compound semiconductor devices.
In production of the compound semiconductor devices, damage occurs on the foregoing interfaces in several production processes. For example, since surface roughness of the compound semiconductor substrate or laminated substrate affects the device characteristics, the surface of the compound semiconductor substrate or laminated substrate is subjected to polishing or etching. This process produces scratches or distortion on the surface to cause damage on the surface. For example, dry etching or wet etching or the like is used in forming a thin film or fine pattern of nanometer size on the surface of the compound semiconductor substrate or laminated substrate. At this time; damage is caused on the surface of the compound semiconductor substrate or laminated substrate or on the surface of the thin film or fine pattern.
When a compound semiconductor device is produced, for example, by growing an epitaxial film on the surface of the compound semiconductor substrate or compound semiconductor membrane with the surface including the damage as described above, the device characteristics are degraded by virtue of the damage existing at the interface between the compound semiconductor substrate or compound semiconductor membrane and the epitaxial film.
Methods for evaluating the damage on the surface of the compound semiconductor substrate or compound semiconductor membrane include methods using X-ray diffraction, scanning electron microscope (SEM), cathodoluminescence, or the like as usually adopted methods.
On the other hand, Japanese Patent Application Laid-Open No. 11-87448 discloses a method of evaluating damage on a substrate by ellipsometry. This method is to evaluate a depth of a damage layer or a level of damage from a change rate of intensity of reflected light from the substrate.
Japanese Patent Application Laid-Open No. 2005-33187 discloses a method of subjecting a wafer to an etching treatment and evaluating a surface structure of the wafer after the etching treatment by ellipsometry. This method is to project polarized light onto the wafer and to evaluate the surface structure of the wafer, using polarized light reflected from the wafer. Specifically, the surface structure of the wafer is estimated from a phase difference Δ and an amplitude ratio ψ between the polarized light projected onto the wafer and the polarized light reflected from the wafer.